Related reading

Less than two weeks after an engine problem grounded all F-35B jump-jet variants, officials believe the problem has been isolated and the jets will soon resume testing.

"The F-35 Joint Program Office and Naval Air Systems Command are developing a return to flight plan which details the removal and inspection requirements of currently installed fueldraulic lines on the 25 F-35B variants affected by the flight suspension," Joe DellaVedova, spokesman for the F-35 Joint Program Office, wrote in a statement.

"The fueldraulic line enables actuator movement for the STOVL vectoring exhaust system," wrote DellaVedova. "Instead of traditional hydraulic fluid, it instead uses fuel as the operating fluid to reduce weight. Stratoflex, the company that produces the line, Rolls-Royce and Pratt & Whitney have instituted corrective actions to improve their quality control processes and ensure part integrity."

"The investigation determined the [fueldraulic] line was improperly crimped," according to DellaVedova. "An audit of quality control records identified six additional non-compliant units which have been removed from aircraft and returned to Pratt & Whitney, the prime contractor for the F-35 propulsion system, for replacement."

"We have begun the process of removing the suspect fueldraulics tubes from the STOVL [short-takeoff, vertical-landing] aircraft, and we are performing additional X-ray imaging inspections on the tubes in order to ensure their integrity," P&W spokesman Matthew Bates wrote. "The team continues to work diligently toward completing the investigation and implementing corrective actions with the supplier. We anticipate a return to flight for the STOVL variant soon."

The STOVL variants were grounded after a Jan. 16 test flight at Eglin Air Force Base was aborted due to engine problem that was later identified as a fueldraulic system failure in the jet.